cursor: mutex S等待事件

cursor: mutex * events等待事件

cursor: mutex * events等待事件用于Cursor Parent 和 Cursor stats类型的操作：

‘Cursor: Mutex S’ ， 某个进程以SHRD S mode申请一个Mutex， 而该Mutex要么被其他进程已EXCL X mode所持有，要么其他进程正在更新mutex 上的Ref Count。

• 相关类型的操作一般是检测父游标或者CURSOR统计信息数据， 此外查询V$SQLSTATS也会造成CURSOR statistics被查询

对父游标parent cursor的检测:

1. 当找到一个游标并准备执行前需要对父游标进行检测。在这个对父游标的检测过程中要用到MUTEX:cursor: mutex S.。
2. 当一个父游标下有很多个子游标时，则服务进程要遍历这些父游标下的子游标以便找到合适的子游标child cursor。
3. 检测的mutex在parent cursor父游标中。

详见 《深入理解Oracle中的Mutex》一文

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Parent examination

• When finding a cursor to execute, the parent must be examined. The examination of the parent is performed using the mutex, cursor: mutex S.
• When the parent cursor has many child cursors involved, this waits will come as the server process has to traverse the entire list of child cursors under the parent to find a match.
• Mutex is in the parent cursor.

A session waits on this event when it is requesting a mutex in shared mode, when another session is currently holding a this mutex in exclusive mode on the same cursor object.

Solutions

Solutions for mutex wait problems are very similar to each other. See Analysis of Waits on Mutexes for more information and troubleshooting ideas.